Quantum Dot (QD), also referring to Nanocrystalline, is a kind of nano-particles consisting of II-VI or III-V group elements, such as CdSe, CdS, CdTe, ZnSe, ZnTe, ZnS and HgTe of II-VI group semiconductor compounds, or InAs and InP of III-V group semiconductor compounds or nano-particles. A Quantum Dot normally has a diameter in a range of 1 nm to 10 nm. Since electrons and holes are quantum confined, a continuous energy band structure becomes a discrete energy level structure with molecule characteristic, and the quantum dot can emit fluorescence after being excited. The emission spectrum of the QDs can be controlled by changing the size of the QDs, and the emission spectrum of the QDs can cover the whole visible region by changing the size and the chemical composition of the QDs. For CdTe QDs, for example, when the diameter of particles is increased from 2.5 nm to 4.0 nm, their emission wavelength can red shift from 510 nm to 660 nm.
Currently, as a light-emitting material, the QDs have been used in some display field. The display device made by using the QDs as the light-emitting material refers to Quantum Dot-Light-emitting Display (QD-LED). Structure of a conventional QD-LED is similar to that of an Organic Light-Emitting Display (OLED). But, compared with the OLED, the QD-LED can exhibit ideally natural colors by changing the size of the QDs. Further, the QD-LED has better color rendering and brightness. Due to these reasons, the QD-LED is attracting more attentions.
Most of the current displays are single-sided displays, with another side of the displays displaying no information. But, under some special situation, such as an information displaying board in a departure hall of an airport, a waiting hall of a train station, or an large exhibition hall, or information displaying board used in a business hall of a service industry such as communication industry, government service, financial industry, or transport industry, a double-sided display is often needed to help the user get the needed information. A conventional double-sided display is often made from two single sided displays attached together back to back, which increases the weight and thickness of products, and also not caters to the trend of lighter, thinner and more portable of modern electronic products.
A feasible solution is to use the QDs as the light-emitting material to make a double-sided display device. But, if a conventional process of QD-LED by layer to layer preparation is used, normally, it needs preparing in turn a transparent anode, a hole transport layer, a quantum light-emitting layer, an electron transport layer, a reflective cathode, or more other layers, which involves numerous of process steps. As such, the preparation efficiency and the yield of the product are low and the production cost is increased.